The objective of the proposed investigation is to study the biochemical parameters of the genetic neurological disorder metachromatic leukodystrophy (MLD). The biochemical defect in MLD is a deficiency of the lysosomal enzyme, arylsulfatase A, which is essential for normal metabolism of cerebroside sulfate a component of myelin. There are several forms of classical MLD and several other forms which are clinically atypical yet show anomalies of arylsulfatase A. The primary experimental model will be fibroblasts in culture derived from normal individuals and patients with the classical and atypical forms of the disorder. All fibroblast strains produce an arylsulfatase A gene product (mutant enzyme); however, depending on the form of disorder they represent, the mutant enzymes vary from no functional catalytic activity to attenuated but experimentally and physiologically significant functional activity. Mutant enzymes will be characterized and compared to normal arylsulfatase A to identify specific anomalies. The properties to be examined include substrate specificity, ratio of enzyme activity to antibody titer, intact cell cerebroside sulfate hydrolyzing capacity, charge properties, microheterogeneity, lectin binding properties, subunit size, and finger-printing. The tissue culture cell system per se will be utilized to examine the natural history of arylsulfatase A (rate of synthesis, half-life, and course of intracellular distribution), manifestations of deficiencies in hydrolysis of substrates other than cerebroside sulfate, and factors associated with enzyme replacement. These studies will provide the basis for early, type specific diagnosis, heterozygote identification and antenatal diagnosis. They should also identify specific anomalies of arylsulfatase A so that appropriate effective therapeutic and/or prophylactic regimen can be rationally developed and tested.